Improper validation of certificate with host mismatch in cURL - CVE-2026-9547

Vulnerability identifier: #VU135089

CSH Severity: Medium

CVSS v4: 6.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-9547

CWE-ID: CWE-297

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to perform a man-in-the-middle attack.

The vulnerability exists due to improper validation of certificate with host mismatch in the CURLOPT_SSH_KEYFUNCTION callback when validating SSH host keys for SCP:// or SFTP:// transfers. A remote attacker can present a host key type that does not match the key type already recorded for the host in the known_hosts file to perform a man-in-the-middle attack.

Only libcurl-based applications built with the libssh backend and using the callback are vulnerable. The curl command line tool is not affected.

cURL
SUSE Linux Enterprise Server 15 SP5
SUSE Linux Enterprise Server 15 SP4
SUSE Linux Enterprise Server 15 SP6
SUSE Linux Enterprise High Performance Computing LTSS 15
SUSE Linux Enterprise High Performance Computing 15
SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise Desktop 15
SUSE Linux Enterprise High Performance Computing ESPOS 15
SUSE Linux Enterprise Server 15
SUSE Linux Enterprise Real Time 15
SUSE Manager Server
SUSE Manager Proxy
SUSE Manager Retail Branch Server
SUSE Linux Enterprise Micro
SUSE Linux Enterprise Micro for Rancher
Ubuntu
Basesystem Module
openSUSE Leap
Anolis OS
Fedora
LANTIME Operating System Firmware (LTOS)
curl (Ubuntu package)
curl-doc
libcurl-minimal
libcurl-devel
libcurl
curl-minimal
curl
libcurl-mini4
libcurl4-32bit-debuginfo
libcurl4-32bit
libcurl4
curl-debuginfo
libcurl4-debuginfo
curl-debugsource
curl-mini-debugsource
libcurl-mini4-debuginfo
libcurl-devel-32bit
curl-zsh-completion
libcurl-devel-doc
curl-fish-completion
libcurl4-64bit
libcurl-devel-64bit
libcurl4-64bit-debuginfo

Install security update from vendor's website.

cURL - update to 8.21.0
LANTIME Operating System Firmware (LTOS) - update to 7.10.013
curl (Ubuntu package) - addressed in versions 7.35.0-1ubuntu2.20+esm20, 7.47.0-1ubuntu2.19+esm16, 7.58.0-2ubuntu3.24+esm9, 7.68.0-1ubuntu2.25+esm4, 7.81.0-1ubuntu1.25, 8.5.0-2ubuntu10.10, 8.14.1-2ubuntu1.4, 8.18.0-1ubuntu2.2
curl-doc - update to 8.4.0-24
libcurl-minimal - update to 8.4.0-24
libcurl-devel - update to 8.4.0-24
libcurl - update to 8.4.0-24
curl-minimal - update to 8.4.0-24
curl - update to 8.4.0-24
libcurl-mini4 - addressed in versions 8.14.1-150400.5.86.1, 8.14.1-150600.4.46.1
libcurl4-32bit-debuginfo - addressed in versions 8.14.1-150400.5.86.1, 8.14.1-150600.4.46.1, 8.14.1-150700.7.20.1
libcurl4-32bit - addressed in versions 8.14.1-150400.5.86.1, 8.14.1-150600.4.46.1, 8.14.1-150700.7.20.1
libcurl4 - addressed in versions 8.14.1-150400.5.86.1, 8.14.1-150600.4.46.1, 8.14.1-150700.7.20.1
curl-debuginfo - addressed in versions 8.14.1-150400.5.86.1, 8.14.1-150600.4.46.1, 8.14.1-150700.7.20.1
libcurl-devel - addressed in versions 8.14.1-150400.5.86.1, 8.14.1-150600.4.46.1, 8.14.1-150700.7.20.1
libcurl4-debuginfo - addressed in versions 8.14.1-150400.5.86.1, 8.14.1-150600.4.46.1, 8.14.1-150700.7.20.1
curl-debugsource - addressed in versions 8.14.1-150400.5.86.1, 8.14.1-150600.4.46.1, 8.14.1-150700.7.20.1
curl - addressed in versions 8.14.1-150400.5.86.1, 8.14.1-150600.4.46.1, 8.14.1-150700.7.20.1
curl-mini-debugsource - addressed in versions 8.14.1-150400.5.86.1, 8.14.1-150600.4.46.1
libcurl-mini4-debuginfo - addressed in versions 8.14.1-150400.5.86.1, 8.14.1-150600.4.46.1
libcurl-devel-32bit - addressed in versions 8.14.1-150400.5.86.1, 8.14.1-150600.4.46.1
curl-zsh-completion - addressed in versions 8.14.1-150400.5.86.1, 8.14.1-150600.4.46.1
libcurl-devel-doc - addressed in versions 8.14.1-150400.5.86.1, 8.14.1-150600.4.46.1
curl-fish-completion - addressed in versions 8.14.1-150400.5.86.1, 8.14.1-150600.4.46.1
libcurl4-64bit - addressed in versions 8.14.1-150400.5.86.1, 8.14.1-150600.4.46.1
libcurl-devel-64bit - addressed in versions 8.14.1-150400.5.86.1, 8.14.1-150600.4.46.1
libcurl4-64bit-debuginfo - addressed in versions 8.14.1-150400.5.86.1, 8.14.1-150600.4.46.1
curl - addressed in versions 8.15.0-8.fc43, 8.18.0-8.fc44

• https://curl.se/docs/CVE-2026-9547.html
• https://github.com/curl/curl/commit/0b8dbbc63c98777e4584cb9

• Multiple vulnerabilities in cURL
• Ubuntu update for curl
• SUSE update for curl
• SUSE update for curl
• SUSE update for curl
• Anolis OS update for curl
• Fedora 44 update for curl
• Fedora 43 update for curl
• Multiple vulnerabilities in Meinberg LANTIME firmware